The present invention relates to a method for the preparation of a layer of a superconducting material with a high transition temperature on the basis of a material system containing metallic components and oxygen. With this method, a layer of a metal oxide preliminary product of the components of the system with a structure which still contains faults with respect to the superconducting metal oxide phase to be developed is first applied to a predetermined substrate with an ordered structure, and subsequently the desired superconducting metal oxide phase is formed epitaxially, using a heat treatment in oxygen. Such a method can be found, for instance, in "Physical Review Letters", Vol. 58, No. 25, June 22, 1987, pages 2684 to 2686.
Films and thin layers of superconducting metal oxide compounds with a high transition temperature T.sub.c of more than 77.degree. K. are generally known. The superconducting metal oxide compounds which contain several metallic components and oxygen can have here in particular a composition of the type Me1--Me2--Cu--0 (Me1=rare earths including yttrium; Me2=earth alkali metals). Films of such material are frequently produced by special vapor deposition or sputtering processes.
Here, a polycrystalline or amorphous preliminary product of the components of the chosen material system is first deposited on a suitable substrate. This preliminary product is subsequently converted into the material with a desired superconducting phase by an annealing treatment which must generally be carried out while oxygen is being supplied. The superconducting metal oxide phases which can be obtained in this manner and the structures of which are similar to that of a perowskite have, in the case of YBa.sub.2 CU.sub.3 0.sub.7-x with 0&lt;x&lt;0.5, an orthorhombic structure (see, for instance, "Europhysics Letters", Vol. 3, No. 12, June 15, 1987, pages 1301 to 1307). Since the materials exhibiting these superconducting phases are similar to oxide ceramics, the corresponding high-T.sub.c superconductors are frequently also designated as oxide-ceramic superconductors.
In addition, it is known from the above-cited publication "Phys. Rev. Lett." to produce monocrystalline films of the system YBa.sub.2 CU.sub.3 O.sub.7-x on a monocrystalline SrTi0.sub.3 substrate by means of epitaxy. To this end the three metallic components of the system are first vapor-deposited on the substrate which exhibits an ordered structure and is at a temperature of about 400.degree. C., from separate evaporation sources in an oxygen atmosphere. The preliminary product obtained in this manner, however, still has a fault structure with respect to the desired superconducting high-T.sub.3 phase. By means of a subsequent heat treatment at a high temperature of about 800.degree.to 900.degree. C. and while oxygen is being supplied, epitaxially grown monocrystalline or at least heavily textured film layers with the desired superconducting high-T.sub.c phase are obtained. Films produced in this manner exhibit a high critical current density j.sub.c of more than 10.sup.5 A/cm.sup.2 at 77.degree.K.
This epitaxy, however, is a necessary condition for reaching such high critical current densities which thereby could also open up wide areas of application for such superconducting films. Thus, for instance, corresponding metallizing layers on semiconducting components are conceivable. The mentioned high-temperature process for developing the desired superconducting high-T.sub.c phase is generally not compatible with the customary process steps for fabricating semiconductor circuits. In addition, the epitaxy proceeding in the high-temperature process is difficult to control since fault-oriented grains are frequently generated which have an adverse effect on the superconducting properties and particularly on the critical current density.